Shock absorber



- E. w L. BEECHER SHOCK ABSORBER- Qriginal Filed June 10,, 1938 flag-wt6. 86801958 ATTORNEY J ing fit in the hydraulic shock absorber I workingor pressure cylinder and a reservoir tor.

' and effectively sealed against Reissued Sept. 30, 1941- UNITED STATESPATENT OFFlCE SHOCK ABSORBER Eugene L. Beecher, Cleveland Heights Ohio,as-

signor to The Gabriel Company, Cleveland. Ohio, a corporation of OhioOriginal No. Serial No.

2,214,038, dated September 10,1940, 212,995, June 10, 1938. Applicationfor reissue October 12, 1940, Serial No. 380,970 g 13 Claims. ,(Cl.188-88) This invention relates to a shock absorber and particularlyto afluid shock absorber.

A shock absorber embodying the present invention may be employed with avariety of machines or apparatus to snub or check the velocity ofmovement between two relatively movable parts thereof, but inasmuch asthe shock absorber oi the present invention has particular adaptabilityand utility when used in motor vehicles, it will be so described herein.

It will also be understood that although the invention is shown appliedto a direct double acting hydraulic shock absorber, certain or all ofits features might be employed in pneumatic shock absorbers or othertypes or hydraulic shock absorbers and his not the intention to limitthe invention to the first named type.

An object of the invention is to provide a hydraulic shock absorberwhich is quiet and eillcient in operation. I

Another object is shock, absorber improved valve means for conto providein a hydraulic,

so constructed that a pneumatic pressure head will be built up in thereservoir during the relative movement of the piston in thecylinder inone direction, and said pressure head will act-to force oil or liquidfrom the reservoir into the working cylinder during the, relativemovement of the piston and cylinder in the opposite direction. Anotherobject is to provide in a fluid shock absorber improved means forassembling and locking a closure member in one end oi the pressure orworking cylinder thereof. Another object is to provide in a directacting shock absorber improved means for preventing the aspiration ofoil or air around the piston rod where it extends through a closure atone end or trolling the displacement of the oil or other liquid in theworking or pressure chamber from one side of the piston to the oppositeside thereof during the operation oi the shock absorber-and which valvemeans is free oi all hissing, whistling, rattling or other sounds.

A further object of the invention is to provide 'in a fluid shockabsorber an improved and novel piston, as well as improved and novelvalve means for controlling the passage of iiuid from one sideto theotherside oi the piston during its movement in one direction and whichpiston is so constructed that it need have only a sliding workcyllnderin which .it operates, as distinguished from a close iit therein, whichiact, together with the iact that the piston does not contact thecylinder wall throughout the entire circumierential area of the piston,reducesthe friction between the p ton and cylinderand consequently thewear on these parts.

A further object is to provide a direct acting oi the type having a theoil or liquid in communication with said cyland reservoir are adequatelythe escape of oil or dust, dirt and that said cylinder liquid therefromor the entrance of other foreign matter the A still further object is toprovide a hydraulic shock absorber of the type having a working orpressure cylinder and a reservoir for the oil or liquid in communicationthe pressure or working cylinder, in combination with improved means forcollecting such oil ioam as may be created at said end of the cylinderand utilizing this foam and the pressure in the cylinder to providepressure lubrication for the piston rod and its bearing in the cylinderclosure.

Further and additional objects and advantages not hereinbeiore referredto will become apparent hereinafter during the detailed descriptionwhich is to follow or an embodiment of the invention.

Referring to the accompanying drawing 11- lustrating said embodiment ofthe invention.

Fig. 1 is a substantially central longitudinal sectional view throughthe shock absorber.

Fig. 2 is a transverse sectional view taken substantially on line 2-2 ofFig. 1 looking in the direction of the arrows.

Fig. 3 is a transverse sectional view through I the working or pressurecylinder and the piston and is taken substantially on line 3-3 of Fig. 1

looking in the direction 0! the arrows.

Fig. 4 is a detached fragmentary elevational view of the lower end oithe pressure or working cylinder 01' the shock absorber, and

Fig. 5 ms transverse sectional view through the pressure or workingcylinder and the piston inder, and which shock absorber-is soconstructed and is taken substantially on line H of Fig. 1"

looking in the direction of the arrows.

The shock absorber embodying the present in-' vention and illustrated inthe accompanying drawing is shown as or the direct double actinghydraulic type and comprises a cylindrical casing III which has relativetelescoping movement within a cylindrical housing II that is spacedradially outwardly irom the casing'll.

. The upper end of the housing II is closed by an invertedcup-shapedclosure or cap member I! and is provided on its outer side with an eyeII therewith, and which is to which the piston rod or the shock absorber(not shown) may be connected, respectively, to

the frame and axle of the vehicle in any suitable manner so as to extendoutwardly therefrom in parallel relation and pass through the eyes 13and I6. These pins or rods may be operatively connected with the eyes l3and It by suitable means well known in the art, wherefore relativemovement between the frame. and axle of the vehicle will cause relativetelescoping movement" between the casing Ill and housingilas will bewell understood.

The pressure or working cylinder I! of the shock absorber is disposedwithin the casing II] in spaced concentric relationship therewith, sothat thespace defined by the casing Ill, cylinder I 1, closure member l5and closure member for the upper end of the casing (later to be referred'to) constitutes a reservoir l8 for the oil or liquid in the shockabsorber.

The lower end of the cylinder ll extends into the cup-shaped member l5and is secured thereto by the end pressure caused by the spinning overof the upper end of the casing Ill. The cylinder l'l upwardly of itslower end has secured therein a closure plate l9. s I

In order to provide an efficient and. economical way for assembling andlocking the closure plate I! in position said plate has itscircumference provided with serrations, wherefore the plate can bepositioned in the cylinder and then 7 the lower end of the cylinder canbe contracted and an annular serrated groove formed therein adjacent theclosure plate IS, with the. result that the serratio is of the plate andgroove interlock and the plate is held in sealing relationship with theinner wall of the cylinder. The cylinder 11 below the serrated groove 20is provided with one or more openings 2| placing that portion of thecylinder below the closure plate I! in communication with the reservoirI8.

The closure plate l9 may be provided with a centrally disposed openingsurrounded by an internally threaded boss 22 and into which a threadedplug 23 is screwed, said plug being provided with a small centrallylocated opening 24 for a purpose later to be explained. The closureplate I 9 also may have secured to its inner side an inwardly projectingfinger 25 that cooperates with an adjustable part carried by the pistonfor the purpose of adjusting the tension of a valve spring as will laterbe explained.

The upper or high pressure end of the cylinder I1 is closed by a plugmember 25 which fits into the cylinder and is suitably secured inposition therein, it being noted that the upper edge of the cylinderis'turned inwardly over the outer side of-"the plug member. providedwith a centrally disposed opening arranged concentrically with acounterbore on the inner side of the member and in which is located aflanged portion of an elastic sleeve 21. The

sleeve 21 is held in position by a thin plate 28 secured to the innerside of the member 26 by suitable means, such as the integral rivet-likeportions 26a that extend through openingsv in The member 28 is the plate28 and then have their ends upset against the plate.

The piston rod l4 extends through the central opening in the member 26and through the elastic sleeve 21. The elastic sleeve 21 tightly gripsthe piston rod and acts as a seal to prevent oil and air working out of*thecylinder I1 along thepiston rod H. In other words, the

elastic sleeve 21 eliminates likelihood of any uncontrolled air passagesbetween the piston rod and the wall of the opening in the member 26. Ifsuch passages existed the result would be an atomization of oil foamthrough the passages to the outside of the cylinder, and this wouldcause an undesirable hissing or whistling noise in the operation of theshock absorber. The elastic sleeve 21 will always tightly grip thepiston rod, and-even though considerable clearance should eventually be.present between the rod and the wall of the opening in the member 26 dueto wear of the parts, the sleeve will still adequately function as aseal to close the passage around the piston.

The plate 28 has its circumference terminating slightly inwardly of thecircumference of the member 25, while said member 28 is providedadjacent its inner side and on its circumference with circularly spacedinclined notches 29 that merge at their upper ends into small grooves30. The grooves 30 have their upper ends in communication with anannular channel 3| formed in the circumference of the member 26substantially midway between the outer and inner ends of the member.Communicating with the channel 3| are a pluralityof circumferentiallyspaced radially extending small passages or bores 32 that terminate inthe central opening of the member 26, see Fig. 2. The purpose of thenotches 29, grooves 30, channel 3| and bores or passages 32 will bepointed outhereinafter.

The upper end 01' the casing I0 is closed by a closure member 33 mountedin the. casing and suitably connected thereto. The closure member 33 isprovided with inwardly extending portions 34 that contact with the upperend of the cylinder IT, as clearly shown in Fig. l. The

member 33 is also provided with a centrally shown in Fig. 1, but sincethis particular detail forms no part of the present invention it is notbelieved necessary to describe the same further- The piston rod ll hassecured to its lower end a piston 33 and said piston on its lower sideis provided with a cylindrical recess 39 at theinner end of which is acentrally located extension 40 that surrounds the lower end of thepiston rod and is lock d thereto. A transverse opening II is formed inthe piston rod H above the piston and communicates with a longitudinallyextending passage 42 that extends to the lower end of the piston rod andis in communication with the recess 33 in thepiston. An externallythreaded cup-shaped plug 43 is screwed into the recess 39 '01 the pistonand the tension of a relatively fstiff coil spring 43b 2 mounted in therecess 3! and having one of its ends abutting against the bottom of thecup-shaped plug 43 serves to lock the plug in its different adjustedpositions.

Rigidly connected to the bottom of the plug a plurality oflongitudinally extending relatively II is a centrally disposed pin 44that extends.

upwardly into .the passage 42 in the piston rod.

. .A small coil spring 45 surrounds the pin 44 and has its upper endabutting against a plate valve 45 that is slidably mounted on the pin Nand is held by the spring it normally seated against the lower end ofthe piston rod and seals the passage .42. 1

broad grooves 54 which are spaced circumferenftially of the piston andwhich, as clearly indicated in Figs. 1 and 5, are of graduallydiminishing depth from a point substantiallymidway of their ends totheir upper ends. The grooves 54,

- however, at their upper ends are not of such This arrangementofthe pin44' and valve 46 possesses a decided advantage. Flap valves .ordinarily.have a tendency to crack open on one side first, with the result thatin order to accommodate the volume of expelled fluid the if the valveshad opened evenly.- This sidewise opening movement of the valves causesvalve flutter and often produced in shock absorbers thumping noises. Theuse of adequate guides for the valves may correct this fault, but theguides cause objectionable weight to be introduced'into'the shockabsorber.

(movement of the valves sidewise is more than' In the presentconstruction the pin 44 has a relatively large diameter, and since itextends into the passage 42 an annular space is provided between the pinand the wall of the passage. Therefore the valve It has an exposedpressure area of annular shape and located substantially near'thecircumference of the valve, wherefore there will be an even pressuredistribution on the valve 45 and the latter will move to and from itsseat in parallel relation to the axis of the pin 44. Also since the areaof the valve is reduced by the area of the pin M a much lighter springpressure is required for the expelled volume of oil.

. A ring 41 also'surrounds the pin II and is for the purpose ofpreventing acomplete collapse of the spring II when the valve It ismoved to 'closed position upon manual adjustment. The

movement of the valve under pressure of the oil is only a fewthousandths of an inch.

The plug member 43 is provided with a plurality of openingsna which canbeeengaged by. the finger I! on the closure member i9 when the piston-isin its most inward position, so that rel-' ative rotation between thecylinder l1 and the piston will cause the member 48 to be screwedinwardly or outwardly of the recess 39. with a resultant change .in thetension of the spring I! and 'consequentlyin the pressure required for.

opening. the valve 4].

A flexible cup packing ring 48, preferably formed of leather, isarranged onthe upper. side of. the piston 88 and is held in positionthereon bytmeans of a plate I! that has a plurality of openings 50'formed therein and through which extend integral pin-like portions Ifformed on.

the upper side of the piston SI. A small passage cates with one; oftheopenings'lll, wherefore the space in the cylinder above the piston-is inconstant communication with the recess 3! and the space in the cylinderbelow the piston. A small It extends through the piston uandcominunidepth as to allow the flexible cup packing 48 to j be forcedinto the grooves by the pressure of the fluid inthe upper part of thecylinder during the operation of the shock absorber, but are soproportioned as to back up the cup packing and prevent such anoccurrence. The aspect or phase of the piston constructionlast'described can be used in hydraulic, pneumatic or other types offluid shock absorbers.

' Assuming that the shock absorber of the construction shown in Fig. land which has Just been described hasits opposite ends connected to theaxle and frame of a motor vehicle, it will be understood that relativemovement of the axle andframe toward each other will cause a relativedownward movement of the piston 38 in the cylinder l1 and, of course, acompression of the vehicle springs. During this relative downwardmovement of the piston 38 in the cylinder H the oil or liquid below thepiston can flow through the passage 52 in the piston to the oppositeside thereof. Also oil will flow through the grooves H in the peripheryof the piston: and its pressure,

will cause it to pass between the flexible cup packing ring 48 and thewall of the cylinder. In addition, some of the oil below the piston andat least in an amount equivalent to the oil displaced by the piston rodll as'the piston moves inwardly of the cylinderwill flow through theopening 24 in the plug 23 and hence through the openingsZiintothereservoir l8. This oil flowing into the reservoir. I8 produces.a compression of the air in the reservoir above the oil level and sincethe upper end of the casing i 0 is thoroughly sealed a relatively highpneumatic pressure head is established at the upper side of thereservoir.

It is desirable in designing shock absorbers to provide for anincreasing built-up resistance at or near the end of the compression orimpact stroke, so that when the shock absorbers are installed onanautomobilethe axle will be prevented in its upward movement under loadimpacts from "bottoming" against the frame of the vehicle. I v

It is contemplatedin constructing shock absorbers embodying thepresent-invention to build intothe shock. absorbers suitable pneumaticpressure heads to provide the desired increasing.

resistance at or near the impact or compression stroke of the shockabsorbers. This may be accomplished as follows:

In finally assembling the shock absorbers the pistons thereof areextended with relation to'the cylinders to themaximum limit of theirextended movement. The correct amount of oil is then introduced into thecylinders and the reserve or reservoir chambers, such that the oil inthe reservoir chambers extends well up into said chambers and thus formstherein an'oil piston and a pneumatic compression chamber above the oilpiston. Then while, the shock absorbersare ,in the extended positionthey are hermetically I sealed, with the result that thepneumaticcompressionchambers above the oil pistons in the reservoirchambers are then at atmospheric pres-'- sure. It will be appreciatedthat different effects of the increasing resistance at or near-the endof 3 Y The piston 38 is provided on its periphery with I the compressionstroke can be obtained by varying the amount of oil introduced into theshock absorber, since the height of the oil in the reservoir or reservechambers will change the effectof the pneumatic compression chamberslocated above the oil pistons.

It will .be understood that if it is desired to cause the pneumaticcompression chamber to be at less than atmospheric pressure when thepiston and cylinder are in the fully extended position that then thehermetical sealing'of the shock absorber need not be made at the fullyextended position. On the other hand, if it is desired to have apneumatic compression chamber which in the fully extended position is atgreater than atmospheric pressure, then gas forming chemicals might beintroduced into the shock absorber,

to bring about this eil'ect.

It will be understood that when the piston rod moves into the cylinderunder an impact stroke,

oil is displaced and flows into-the reservoir cham- I her and causes theoil therein to rise into the space which forms the pneumatic compressionchamber. This raises the pressure of air or gas and results in apneumatic resistance which supplements the hydraulic resistance, andeventually as the end of the impact or collapsing strok approaches thepneumatic resistance will have been built up to a resistance greaterthan the hydraulic resistance and will act-to prevent bottoming of theaxle.

In installing shock absorberson automobiles it is the general practiceto allow more recoil stroke ithan compression or impact stroke in thenormal or riding position. Therefore, on a shock absorber having a totalstroke or six inches, for

example, the piston could be moved approximately four inches on therecoil stroke and two inches on the compression or impact stroke and thepneumatic compression chamber would be considerably above atmosphericpressure at the normal riding position. 7

' It will be noted that in addition to the piston being provided with afixed passage through which the oil can flow from one side of the piston to the other during its movement in either direction, it is alsoprovided with valve means for allowing a greater flow of oil from oneside of the piston to the other when the piston is moving downwardly inthe cylinder, that is toward the low pressure'end than is the case whenit is moving upwardly toward the high pressure end.

This valve means being formed of the flexible cup packing l8 and thegrooves 54 is highly ellicient, and since there are no movable metalparts the valve means is totally quiet in operation. In addition, thepiston 38 only has portions of its periphery in engagement with the wallof thecylinder, that is the portions'intermediate the grooves 54,wherefore friction between the piston and cylinder is at a minimum thusreducing the relative wear between the parts.' Likewise, because of theuse of the flex-- ible cup packing 48 his unnecessary to provide asclose or tight a fit between the piston and cylinder as would ordinarilybe the case.

As the piston moves upwardly in the cylin- "der any oil foam oremulsification of the oil above the piston caused by the compression ofthe entrained air therein will-pass through the grooves 29 and into theannular chamber 3! in the member'26.- In other words, the chamber IIwill act as a collecting chamber '1 r 011' foam and the pressures in thecylinder and in the chamber 3| will cause small quantities of, this oilfoam to be forced under pressure through the small passages or bores 32against the piston rod I, thus providing forced or pressure lubricationfor the rod. During the downward movementof the piston in thecylinderQoil which has accumulated I in the chamber II will be drawnbacklnto the cylinder.

From the foregoing a hydraulic shock absorber embodying the pres- Whenthe axle and the frame of the vehicle start to separate or move away.from each other" under the recoil actionv of the vehicle spring, thepiston 38, of course, moves relatively upwardly in the cylinder l-I. Asthe piston moves upwardly the pneumatic pressure head in the reservoiracts on the oil therein to force the same through the opening I4 andinto the cylinder below the piston, thus eliminating any tendency for avacuum to be created below the piston in the lower 1 end of thecylinder. The oil in the cylinder above the piston as the piston movesupwardly can at first only now to the lower side of the piston thepressure of the oil in the flexible cup-shaped pecking 48 causes saidpacking to tightly engage the wall of the cylinder and prevent any flowof 011 between the packing and the cylinder'and e oftheoil in the mainsseated until the pro in the opening 41 upper end of the cylinder a andpassage ll reaches a predetermined point sumcient to ovorcome'thetension of the spring through the passage n, it being understood thatthrough thegrooves I. Also during this upward Q movement of the pistonthe plate valve 40 rewhereupon the valve it will unseat and allow thishigh prcssureoil to now from the passage '42 to the other side otthepiston. As previously stated, the tension of the spring ll can be nd-,

iusted without the necessity of removing the iston from the cylinder by"merely enema v fliigerllofthecloniromember llinanopenins' "a of the plugmember 0. and then relatively ent invention will be quiet and eflicientin 013- eration and that the valve means for controlling thedisplacement of the oil or other liquid in the working or pressurechamber from one side of I the pistonto the opposite side thereof willbe free of. hissing. Whistling, rattling or other sounds. 'It willalsobe seen that the piston is of improved and novel construction, aswell as the valve means associated therewith for controlling the passageof fluid thereby in one direction.

The construction of the piston and valve means is such that the pistonneed-have only a sliding working lit in the cylinder as distinguishedfrom A a close flt' therein, which fact together with the fact that thepiston does not contact the cylinder, wall throughout the entirecircumferential area of the piston reduces the friction between thepiston and cylinder and consequently thewear on these parts;

Although a preferred embodiment of the in-- vention has been illustratedand described here- 1 in, it will be understood that the invention issusceptible of various modificationsand adaptations within the scope ofthe appended claims.

Having thusdescribed my invention, I claim: '1. A hydraulic shockabsorber comprising relatively reciprocablecylinder and pistonmembers;said piston memberlbeing' provided with a passage extending between theopposite ends" there- 01', a flexible cup shapod packing ring carried bywe piston and overlying one end of menu sage and having its wall'portlon e suing the lit will have been seen that i cylinder, a closureplug der provided with a centrally dis cylinder wall whereby said ringseals said passage during movement of the piston in one direction, saidpiston being provided with a second and constantly open passageextending therethrough, said piston also being provided with a a pistonrelatively reciprocablein said cylinder and provided with a rodextending through said centrally disposed opening, said closurepiugbeing provided intermediate. its ends with an anthird passagetherethrough, and a spring controlled valve sealing said third passagewhen the pressure of the liquid therein is below a predetermined pointduring movement 01' said piston in said one direction.

2. A shock'absorber comprising a cylinder, a

nular peripheral groove torming a chamber and with a port extendingradially from said central 4 opening to said chamber, said closure plugalso piston relatively reciprocable therein and provided with aperipheral passage extending from end to end thereof and having aportion adjacent one end of said piston or gradually diminishing depth,and a flexible cup-shaped packing ring mounted on said end of saidpiston and being provided with'a relatively small passage placing saidchamber'in communication with said cylinder.

8., A hydraulic shock absorber comprising a cylinder, a closure plug forone end of the cylinder and provided with a centrally disposed openingand with an elastic sleeve extending 1m wardly oi the cylinder andaligned with said opening, a piston relatively reciprocable in saidoverlying the end 01 said portion of. said passage and having its wallportion engaging the cylinder wall. whereby said ring seals said passageduring movement of the piston in one direction.

3. A shock absorber comprising a cylinder, a piston relativelyreciprooable therein and provided with aplurality of oircumferentiallyspaced peripheral grooves extending from end to end of the piston and ofgradually diminishing depth adjacent one end of the latter, and aflexible cupshaped packing ring mounted on said end of said piston andoverlying said grooves and having its wall portion engaging the'cylinderwall whereby said ring seals said grooves during movement oi the pistonin one direction.

- 4. A hydraulic shock absorber comprising a cylinder, 9. pistonrelatively reciprocable therein and provided with a plurality ofcircumferentially spaced peripheral grooves extending irom end to end ofthe piston, a flexible cup-shaped packing ring mounted on one end saidpiston and overlying one end of said grooves and having its wall portionengaging the cylinder wall whereby said ring seals said grooves duringmovement oi the piston in one direction, said piston being provided withpassages therethrough one of which is constantly open and anothernormally closed, and a spring controlled valve sealing said last namedpassage when the pressure of the liquid therein is below a predeterminedpoint.

5. A shock absorber comprising a cylinder, a

- piston relatively reciprocable therein and pro-- vided witha pluralityof longitudinal peripheral recesses oi! relatively broad width extendingirom end to end oi the piston and spaced circumferentially thereof, saidrecesses being of gradually diminishing depth toward one end of saidpiston, and a flexible cup-shaped packing ring mounted on said end ofsaid piston and overlying the end of said recesses and'having its wallportion engaging ring seals said recesses piston in one direction.

during movement 01 the 6. A hydraulic shock absorber comprisinga plug atone o! munication with said cylinder.

'7. A hydraulic shock absorber comprising a at one end of saidcylincylinder and provided with a piston rodextending through saidsleeve and said opening, said closure plug being provided intermediateits ends with an annular peripheral groove forming a chamber and with aport extending radially from said opening to said chamber, said closureplug also being provided with a'relatively small peripheral passageplacing said chamber in communication with said cylinder.

9; A shock absorber comprising relatively reciprocable cylinder andpiston members, a closure member for one end of said cylinder andprovided on its circumference with serrations, said cylinder havingformed therein adjacent said closure member an internal annular serratedgroove the serrations 01 said groove and said closure member beinginterlocked to retain the latter inposition.

10. In a hydraulic shock absorber, a cylinder, a piston relativelymovable in the cylinder and provided with a passage'extending through itand having at one of its ends a valve seat, a

, pin carried bysaid piston and extending into said one end of saidpassage, and providing a predetermined annular space between theperiphery oi the pin and the wall of the passage, a disk valve mountedon said pin, and a spring acting on said valve, and maintaining the samenormally seated against said valve seat.

11. In a direct acting hydraulic shock ah- I sorber, an elongatedcylinder, a piston reciprocable therein, a rod extending into thecylinder the cylinder wall whereby said at one end thereof Ior actuatingthe piston, a reservoir having restricted communication with thecylinder adjacent its other end and into which liquid is forced bymovement of said rod into the cylinder, said pistonhaving peripheralgrooves extending from end to end thereof for flowing liquid past thepiston upon movement of the latter toward saidother end 0'! thecylinder, aflexible cup-shaped packing mounted on the piston andoverlying oneend of said grooves and having its annular wall portionengaging the cylinder wall whereby said packing seals said groovesduring movement oi the piston toward said one end of the cylinder,-saidpiston also having a constantly open passage of restricted size thereinplacing in communication the cylinder. posed opening, 12. In a directwith each other the portions of the cylinder on opposite sides of thepiston and a third passage of relatively larger size also connectingsaid cylinder portions with each other, and a spring controlled valvesealing said third passage during movementof the piston toward saidother end of the cylinder and adapted to be unseated by apredeterminedpressure of the liquid during movement oi! the piston toward said oneend of acting hydraulic shock abgrooves during movement of the said oneend of ,the cylinder.

sorber. an elongated cylinder, a piston reciprocable therein, a rodextending into the cylinder at one end thereof for actuatingth'cpiston,a

reservoir having restricted communication with the cylinder adjacentitssother end and into which liquid is forced by movement of said rodinto the cylinder, said piston having peripheral grooves extending fromend to end thereof and of gradually diminishing depth for flowing liquidpast the piston upon movement 0! the latter 10 toward said other endot-the cylinder, and a flexible cup-shaped packing mounted on the pistonand overlying one end oi. said grooves and having its annular wallportion engaging the cylinder wall whereby said packing seals saidpiston toward 13. A hydraulic shock absorber comprising relativelyreciprocable cylinder and piston members, said piston member beingarranged in and contacting said cylinder and being provided with apassage therethrough which has one of its ends terminating at theperiphery of the piston, said piston also being-provided with a secondand constantly open passage therethrough. said passages placing theportions of the cylinder on opposite sides oi'said piston incommunication passage, means associated with one of said membars andproviding a third passage placing the portions of the cylinder onopposite sides 0! the piston in communication with each other, and aspring controlled valve sealing said third passage when the pressure oitheliquid therein is 20 below a predetermined point.

